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Active Deformation (active + deformation)
Selected AbstractsGeomorphic constraints on the active tectonics of southern TaiwanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007Lucy A. Ramsey SUMMARY Taiwan is a region of rapid active tectonics, yet the study of the tectonic processes that shape the interior of the island is difficult due to the high rates of erosion and dense vegetation. We use digital topography to look for indications of active deformation preserved in the local geomorphology. In particular, anomalies in the regional pattern of drainage are used to infer zones of enhanced tectonic activity. The apparent anticlockwise rotation of major river systems in plan view indicates the presence of a diffuse zone of left-lateral shear running down the southeastern side of Taiwan. Asymmetries in the catchments of individual drainage basins show the influence of varying rates of uplift across southern Taiwan, with the most rapid uplift close to Taitung at the indentation point of the Luzon arc with the Chinese continental margin. Our interpretations, though based predominantly on remote-sensing observations, are consistent with the available field evidence. This study demonstrates the usefulness of drainage basins as tectonic markers in the quantification of regional strain and uplift, which may have wider applicability in other deforming parts of the world. [source] Hydrothermal alteration, fluid flow and volume change in shear zones: the layered mafic,ultramafic Kettara intrusion (Jebilet Massif, Variscan belt, Morocco)JOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2004A. Essaifi Abstract During emplacement and cooling, the layered mafic,ultramafic Kettara intrusion (Jebilet, Morocco) underwent coeval effects of deformation and pervasive fluid infiltration at the scale of the intrusion. In the zones not affected by deformation, primary minerals (olivine, plagioclase, clinopyroxene) were partially or totally altered into Ca-amphibole, Mg-chlorite and CaAl-silicates. In the zones of active deformation (centimetre-scale shear zones), focused fluid flow transformed the metacumulates (peridotites and leucogabbros) into ultramylonites where insoluble primary minerals (ilmenite, spinel and apatite) persist in a Ca-amphibole-rich matrix. Mass-balance calculations indicate that shearing was accompanied by up to 200% volume gain; the ultramylonites being enriched in Si, Ca, Mg, and Fe, and depleted in Na and K. The gains in Ca and Mg and losses in Na and K are consistent with fluid flow in the direction of increasing temperature. When the intrusion had cooled to temperatures prevailing in the country rock (lower greenschist facies), deformation was still active along the shear zones. Intense intragranular fracturing in the shear zone walls and subsequent fluid infiltration allowed shear zones to thicken to metre-scale shear zones with time. The inner parts of the shear zones were transformed into chlorite-rich ultramylonites. In the shear zone walls, muscovite crystallized at the expense of Ca,Al silicates, while calcite and quartz were deposited in ,en echelon' veins. Mass-balance calculations indicate that formation of the chlorite-rich shear zones was accompanied by up to 60% volume loss near the centre of the shear zones; the ultramylonites being enriched in Fe and depleted in Si, Ca, Mg, Na and K while the shear zones walls are enriched in K and depleted in Ca and Si. The alteration observed in, and adjacent to the chlorite shear zones is consistent with an upward migrating regional fluid which flows laterally into the shear zone walls. Isotopic (Sr, O) signatures inferred for the fluid indicate it was deeply equilibrated with host lithologies. [source] Influence of the mechanical behaviour of brittle,ductile fold,thrust belts on the development of foreland basinsBASIN RESEARCH, Issue 2 2010Guy D. H. Simpson ABSTRACT A two-dimensional mathematical model considering coupling between a deforming elasto-visco-plastic fold,thrust belt, flexural subsidence and diffusional surface processes is solved using the Finite Element Method to investigate how the mechanical behaviour of brittle,ductile wedges influences the development of foreland basins. Results show that, depending mainly on the strength of the basal décollement, two end-member types of foreland basin are possible. When the basal detachment is relatively strong, the foreland basin system is characterised by: (1) Highly asymmetrical orogen formed by thrusts concentrated in the incoming pro-wedge. (2) Sedimentation on retro-side takes place in one major foredeep basin which grows throughout orogen evolution. (3) Deposition on the pro-side occurs initially in the foredeep, and continues in the wedge-top before isolated basins are advected towards the orogen core where they become uplifted and exhumed. (4) Most pro-wedge basins show an upward progression from low altitude, foredeep deposits at the base to high altitude, wedge-top deposits near the surface. In contrast, when the basal detachment behaves weakly due to the presence of low viscosity material such as salt, the foreland basin system is characterised by (1) Broad, low relief orogen showing little preferential vergence and predominance of folding relative to faulting. (2) Deposition mainly in wedge-top basins showing growth strata. (3) Many basins are initiated contemporaneously but form discontinuously due to the locus of active deformation jumping back and forth between different structures. Model results successfully reproduce first order observations of deforming brittle,ductile wedges and foreland basins. Moreover, the results support and provide a framework for understanding the existence of two main end-member foreland basin types, simple and complex, associated with fold,thrust belts whose detachments are relatively strong and weak, respectively. [source] Distribution of Palaeozoic reworking in the Western Arunta Region and northwestern Amadeus Basin from 40Ar/39Ar thermochronology: implications for the evolution of intracratonic basinsBASIN RESEARCH, Issue 3 2009Sandra McLaren ABSTRACT The Centralian Superbasin in central Australia is one of the most extensive intracratonic basins known from a stable continental setting, but the factors controlling its formation and subsequent structural dismemberment continue to be debated. Argon thermochronology of K-feldspar, sensitive to a broad range of temperatures (,150 to 350 °C), provides evidence for the former extent and thickness of the superbasin and points toward thickening of the superbasin succession over the now exhumed Arunta Region basement. These data suggest that before Palaeozoic tectonism, there was around 5,6 km of sediment present over what is now the northern margin of the Amadeus Basin, and, if the Centralian superbasin was continuous, between 6 and 8 km over the now exhumed basement. 40Ar/39Ar data from neoformed fine-grained muscovite suggests that Palaeozoic deformation and new mineral growth occurred during the earliest compressional phase of the Alice Springs Orogeny (ASO) (440,375 Ma) and was restricted to shear zones. Significantly, several shear zones active during the late Mesoproterozoic Teapot Orogeny were not reactivated at this time, suggesting that the presence of pre-existing structures was not the only controlling factor in localizing Palaeozoic deformation. A range of Palaeozoic ages of 440,300 Ma from samples within and external to shear zones points to thermal disturbance from at least the early Silurian through until the late Carboniferous and suggests final cooling and exhumation of the terrane in this interval. The absence of evidence for active deformation and/or new mineral growth in the late stages of the ASO (350,300 Ma) is consistent with a change in orogenic dynamics from thick-skinned regionally extensive deformation to a more restricted localized high-geothermal gradient event. [source] Evolution of the late Cenozoic Chaco foreland basin, Southern BoliviaBASIN RESEARCH, Issue 2 2006Cornelius Eji Uba ABSTRACT Eastward Andean orogenic growth since the late Oligocene led to variable crustal loading, flexural subsidence and foreland basin sedimentation in the Chaco basin. To understand the interaction between Andean tectonics and contemporaneous foreland development, we analyse stratigraphic, sedimentologic and seismic data from the Subandean Belt and the Chaco Basin. The structural features provide a mechanism for transferring zones of deposition, subsidence and uplift. These can be reconstructed based on regional distribution of clastic sequences. Isopach maps, combined with sedimentary architecture analysis, establish systematic thickness variations, facies changes and depositional styles. The foreland basin consists of five stratigraphic successions controlled by Andean orogenic episodes and climate: (1) the foreland basin sequence commences between ,27 and 14 Ma with the regionally unconformable, thin, easterly sourced fluvial Petaca strata. It represents a significant time interval of low sediment accumulation in a forebulge-backbulge depocentre. (2) The overlying ,14,7 Ma-old Yecua Formation, deposited in marine, fluvial and lacustrine settings, represents increased subsidence rates from thrust-belt loading outpacing sedimentation rates. It marks the onset of active deformation and the underfilled stage of the foreland basin in a distal foredeep. (3) The overlying ,7,6 Ma-old, westerly sourced Tariquia Formation indicates a relatively high accommodation and sediment supply concomitant with the onset of deposition of Andean-derived sediment in the medial-foredeep depocentre on a distal fluvial megafan. Progradation of syntectonic, wedge-shaped, westerly sourced, thickening- and coarsening-upward clastics of the (4) ,6,2.1 Ma-old Guandacay and (5) ,2.1 Ma-to-Recent Emborozú Formations represent the propagation of the deformation front in the present Subandean Zone, thereby indicating selective trapping of coarse sediments in the proximal foredeep and wedge-top depocentres, respectively. Overall, the late Cenozoic stratigraphic intervals record the easterly propagation of the deformation front and foreland depocentre in response to loading and flexure by the growing Intra- and Subandean fold-and-thrust belt. [source] Recent tectonics in the Turkana Rift (North Kenya): an integrated approach from drainage network, satellite imagery and reflection seismic analysesBASIN RESEARCH, Issue 2 2004W. Vétel The Turkana rifted zone in northern Kenya is a long-lived and polyphased rift system where the lack of well-marked rift morphology makes it difficult to identify the zone of active deformation. A high-density river network is exceptionally well developed over the study area and shows evidence of drainage anomalies that suggest recent fault-induced movements at various scales. Correlation of surface drainage anomalies with Landsat remote sensing and deep seismic reflection data permits to characterize the deep geometry of the inferred fault structures. Seismic stratigraphy further allows distinction between the inherited (Oligocene,Pliocene) and the newly formed (<3.7 Ma) origin of the recent deformation. Evidence for neotectonics are observed (1) along a large-scale transverse (EW) fault rooted at depth along a steep basement discontinuity (Turkwell), (2) along a rift-parallel (NS) fault zone probably emplaced during the Pliocene,Pleistocene and currently bounding the Napedet volcanic plateau to the west and (3) over a round-shaped uplifted zone caused by positive inversion tectonics (Kalabata). The major contribution of this work is the recognition of a broad (80 km wide) zone of recent/active extensional deformation in the Turkana Rift in contrast with the narrow (20 km wide) N10°E-trending axial trough forming the Suguta valley to the south, and the Chew Bahir faulted basin to the north. These along-strike variations in structural style are partly controlled by the occurrence of rejuvenated Oligocene,Miocene rift faults and long-lived transverse discontinuities in the Turkana Rift area. More generally, this study has implications for the use of river drainage network about recent/active extensional domains with subdued topography and slow deformation rate. [source] | ||||||||||